U.S. patent application number 14/622990 was filed with the patent office on 2015-06-11 for intumescent coating compositions.
This patent application is currently assigned to Sherwin-Williams Protective & Marine Coatings. The applicant listed for this patent is Sherwin-Williams Protective & Marine Coatings. Invention is credited to William Allen, John Darryl Green, Andrew Philip Taylor.
Application Number | 20150159368 14/622990 |
Document ID | / |
Family ID | 34112988 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150159368 |
Kind Code |
A1 |
Green; John Darryl ; et
al. |
June 11, 2015 |
INTUMESCENT COATING COMPOSITIONS
Abstract
A coating system comprising: (1) a liquid intumescent coating
composition comprising a resin system comprising at least one
polymeric component, at least one ethylenically unsaturated
monomeric component, and at least one intumescent ingredient, the
coating composition being curable to a solid state by free radical
polymerisation, and (2) a reinforcement structure. The
reinforcement structure may comprise any of mesh, fabric and/or
tape. The reinforcement structure preferably comprises an inorganic
fabric, and may be installed by application of a suitable adhesive
binder.
Inventors: |
Green; John Darryl;
(Lancashire, GB) ; Allen; William; (Lancashire,
GB) ; Taylor; Andrew Philip; (Lancashire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sherwin-Williams Protective & Marine Coatings |
Lancashire |
|
GB |
|
|
Assignee: |
Sherwin-Williams Protective &
Marine Coatings
Lancashire
GB
|
Family ID: |
34112988 |
Appl. No.: |
14/622990 |
Filed: |
February 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11722348 |
Feb 20, 2009 |
|
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|
PCT/GB2005/005043 |
Dec 21, 2005 |
|
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14622990 |
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Current U.S.
Class: |
52/232 |
Current CPC
Class: |
C09D 133/04 20130101;
C09D 5/185 20130101; E04B 1/945 20130101; B32B 2419/00 20130101;
E04B 1/941 20130101; C08L 2201/02 20130101; B32B 15/04
20130101 |
International
Class: |
E04B 1/94 20060101
E04B001/94; B32B 15/04 20060101 B32B015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2004 |
GB |
0428009.5 |
Claims
1. A fire resistant steel structure comprising: (1) a steel
substrate; (2) a reinforcement structure positioned on said steel
substrate; and (3) a liquid intumescent coating composition applied
to said substrate, said liquid intumescent coating composition
comprising a resin system comprising at least one polymeric
component, at least one ethylenically unsaturated monomeric
component, at least one intumescent ingredient and a chemical
initiator for initiating a reaction to cure the coating composition
to a solid state by free radical polymerization.
2. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure comprises at least one of mesh,
fabric and tape.
3. The fire resistant steel structure as recited in claim 2,
wherein the reinforcement structure comprises an inorganic
fabric.
4. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure is woven or knitted.
5. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure comprises at least one
inorganic material.
6. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure comprises any of the following,
either alone or in combination: galvinized steel wire mesh, glass
and silica.
7. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure comprises organic material.
8. The fire resistant steel structure as recited in claim 7,
wherein the reinforcement structure comprises any of the following
either alone or in combination: carbon fibre and aramid fibre.
9. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure is provided between two
different layers of the coating composition.
10. The fire resistant steel structure as recited in claim 1,
wherein the intumescent coating composition is applied to the solid
steel substrate and the total thickness of the cured intumescent
coating composition is in the range from 0.25 mm to 20 mm.
11. The fire resistant steel structure as recited in claim 1,
wherein the said at least one polymeric component comprises solid
thermoplastic resin.
12. The fire resistant steel structure as recited in claim 1,
wherein the at least one polymeric component comprises at least one
homopolymer, copolymer and/or terpolymer of a methacrylate
resin.
13. The fire resistant steel structure as recited in claim 1,
wherein the at least one polymeric component comprises a
meth(acrylate) copolymer.
14. The fire resistant steel structure as recited in claim 1,
wherein the at least one polymeric component comprises the reaction
product of at least one styrene or vinyl toluene together with at
least one of any of the following: methyl methacrylate, ethyl
methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl
methacrylate, 2-hydroxy ethyl methacrylate 2-hydroxy propyl
methacrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl
acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2
hydroxy ethyl acrylate, 2-hydroxy propyl acrylate and 2-ethylhexyl
acrylate.
15. The fire resistant steel structure as recited in claim 1,
wherein the at least one polymeric component comprises the reaction
product of one or more diene together with at least one of any of
the following: styrene, vinyl toluene, vinyl chloride, vinyl
acrylate, vinylidine chloride, and vinyl versatate esters.
16. The fire resistant steel structure as recited in claim 1,
wherein the ethylenically unsaturated monomeric component has at
least one of a methacrylate or acrylate functionality.
17. The fire resistant steel structure as recited in claim 1,
wherein the ethylenically unsaturated monomeric component comprises
any of the following either alone or in combination: methyl
methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl
methacrylate, t-butyl methacrylate, 2-hydroxy ethyl methacrylate
2-hydroxy propyl methacrylate, 2-ethylhexyl acrylate, methyl
acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
t-butyl acrylate, 2 hydroxy ethyl acrylate, 2-hydroxy propyl
acrylate and 2-ethylhexyl acrylate.
18. The fire resistant steel structure as recited in claim 1,
wherein the resin system constitutes from 20% to 60% of the coating
composition.
19. The fire resistant steel structure as recited in claim 1,
wherein said at least one intumescent ingredient comprises an acid
source, a carbon source and a gas source.
20. The fire resistant steel structure as recited in claim 1,
wherein the chemical initiator is selected from AZO compounds or
organic peroxides.
21. The fire resistant steel structure as recited in claim 1,
wherein the chemical initiator is selected from diacyl peroxides,
ketone peroxides, peroxyesters, dialkyl peroxides, hydroperoxides,
and peroxyketals.
22. The fire resistant steel structure as recited in claim 1,
wherein the reinforcement structure comprising a series of rows of
interlocking fibers oriented such that said rows of fibers
intersect each other at approximately 90.degree..
Description
[0001] The present invention relates to liquid intumescent coating
compositions that have particular, but not exclusive, application
in protecting steel structures in a fire situation.
[0002] Intumescent coating compositions are commonly used to
protect structural steel components in buildings (or any other
steel supported structure) against the effects of any fire
conditions known to the art including cellulosic, hydrocarbon
and/or Jetfire conditions. They contain a resin system "pigmented"
with various intumescent ingredients that under the influence of
heat, react together to produce an insulating foam or "char",
having low thermal conductivity, which has a volume many times that
of the original coating. This char greatly reduces the rate of
heating experienced by the steel, thus extending the time before
the steel loses its integrity and the building/structure collapses,
thereby allowing additional time for safe evacuation.
[0003] During a fire situation, a steel structure will heat up, the
rate of heating depending on the specific dimensions of the steel
sections used in the structure. The rate of heating is dependent on
the Hp/A value of the section, where Hp is the perimeter of the
steel when viewed in cross-section, and A is the cross-sectional
area.
[0004] A steel section with a large perimeter (Hp) will receive
more heat than one with a smaller perimeter. On the other hand, the
greater the cross-sectional area (A), the more heat the steel
section can absorb. Thus, a large thin steel section having a high
Hp/A value will heat up more quickly than a small thick section
having a lower Hp/A value.
[0005] The thickness of the coating that is applied depends on the
Hp/A value of the steel, its configuration, and the level of fire
protection required. The latter is typically specified from 30
minutes to 120 minutes, this being the time taken for the steel to
reach its critical failure temperature (550.degree. C.) under
standard test conditions. It should be noted that variations do
occur in failure temperature criteria, for example, if the steel
section is in a horizontal plane (beam) opposed to a vertical plane
(column) then the failure temperature is usually higher (around
620.degree. C. compared to 550.degree.). Also, different failure
criteria exist depending on the test procedure being used, for
example if a hydrocarbon fire situation is being evaluated,
commonly an extra safety margin is built in and a failure
temperature of 400.degree. C. is used.
[0006] Typically the dry film thickness of intumescent coating
applied varies from 250 .mu.m to several millimetres, depending on
the level of fire protection required. With solvent based or water
based prior art intumescent coatings, the higher dry film
thicknesses can only be achieved by the application of multiple
coats.
[0007] Prior art intumescent coatings designed for cellulosic fire
protection tend to be based on high molecular weight thermoplastic
resins based on acrylate, methacrylate and/or vinyl chemistry and
require a high proportion of organic solvent or water to facilitate
application to the substrate to be fire protected. This leads to
slow and often protracted drying times, especially when high wet
film thicknesses are applied (up to 2 mm per coat), since the rate
of drying is dependent on the evaporation of the carrier solvent.
Increasingly stringent legislation concerning organic solvent
emissions has meant greater use of water based products but slow
drying remains a problem, particularly when the relative humidity
is high.
[0008] Where multiple coats are required the problems of slow
drying are exacerbated, particularly with solvent based coatings,
where solvent from subsequent coats can strike back into the
previous coats.
[0009] The use of ovens or near infra-red heaters can reduce the
drying times, though these are expensive to operate, and due to the
thermoplastic nature of the coatings, cooling is necessary prior to
handling in order to prevent damage. Cooling of thick heavy steel
sections, can take a relatively long time.
[0010] Prior art intumescent coatings designed for hydrocarbon and
Jetfire fire scenarios have tended to be 100% solids (i.e. no
volatiles present) and based on epoxy resin systems, giving rise to
high viscosity mastic type coatings. The epoxy binder system of
this type of coating provides excellent durability to adverse
weather conditions and also, its thermoset resin backbone gives
rise to a very dense, hard intumescent char which is ideally suited
to give steel protection from the hotter, harsher more turbulent
hydrocarbon and jetfire fires.
[0011] Unfortunately, the high viscosity of mastic type coatings of
the above type tends to lead to difficulties to apply the coatings
by conventional methods, with sophisticated plural component spray
systems usually being required. Also significantly higher film
thicknesses of said coatings tend to be required to insulate steel
to hydrocarbon fires compared to their cellulosic equivalents,
typically up to 10 times higher thickness of epoxy based mastic
intumescent can be required to protect, for example, a steel column
for 60 minutes hydrocarbon fire, compared to a cellulosic product
in a cellulosic fire. Prior art hydrocarbon fire protection
products also tend to require the incorporation of some form of
reinforcement sandwiched between coats of the product. This
reinforcement usually takes the form of a metal or synthetic mesh
or cloth, and is required to enhance the performance of the
intumescent char in a fire All of the above has meant that
hydrocarbon fire protection of steel structures has tended to be
significantly more expensive than cellulosic fire protection for
the same time periods.
[0012] Jetfire scenarios have an even greater destructive erosive
effect than hydrocarbon fires. For this reason, char integrity
becomes all important. A state of the art cellulosic fire
protection system expands typically to 25-100 times its original
volume forming a weak fluffy char that is easily destroyed by
jetfire conditions. State of the art hydrocarbon/Jetfire fire
materials expand by a factor of typically 2-8 times thus forming a
tougher harder char that is more able to cope with the erosive
nature of jetfire.
[0013] Traditionally, intumescent coatings were applied on-site to
steel structures during the construction phase of the building.
More recently in-shop application has become more common practice,
as better control of application conditions is possible. Slow
drying means that throughput is compromised, as coated steel
sections cannot be moved until they are hard enough to resist
damage.
[0014] The present invention seeks to provide a relatively
quick-drying intumescent coating system.
[0015] According to a first aspect of the present invention there
is provided a coating system comprising:-- [0016] (1) a liquid
intumescent coating composition comprising a resin system
comprising at least one polymeric component, at least one
ethylenically unsaturated monomeric component, and at least one
intumescent ingredient, the coating composition being curable to a
solid state by free radical polymerisation, and [0017] (2) a
reinforcement structure. [0018] The reinforcement structure may
comprise any of mesh, fabric and/or tape. The reinforcement
structure preferably comprises an inorganic fabric. The
reinforcement is preferably installed by application of a suitable
adhesive binder.
[0019] The use of a reinforcement mesh or cloth has been
demonstrated to give improved fire protection for the present
invention for situations requiring relatively high film
thicknesses, for example greater than 4-5 mm of coating, which
would be required for longer periods of fire protection, for
example 2 hours and above, or for certain hydrocarbon and jetfire
scenarios. A reinforcement structure can also be used at lower film
thicknesses of coating, but the improvement effects will be less
apparent. The reinforcement preferably takes the form of a woven or
knitted mesh based upon non-combustible materials which are
predominantly inorganic. There are many examples known to the art
including, but not limited to inorganics such as galvanised steel
wire mesh, glass or silica fibre, and stainless steel wire and
organics such as carbon fibre, aramid fibre and other polymer
yarns. The reinforcement preferably comprises a series of rows of
interlocking fibres or filaments orientated such that rows of said
fibres or filaments intersect at approximately 90.degree. to each
other i.e. perpendicular The spaces between each row of fibres or
filaments should preferably be between 1 mm and 20 mm.
[0020] The reinforcement can be applied over the entire perimeter
of the steel section, or only to a selected part of the perimeter.
The reinforcement is typically applied into the film at the
interface of two layers of coating. It is normally applied onto the
surface of a partially cured, pliable, layer and pressed into that
layer by roller application. In certain scenarios the mesh and/or
fabric is held in place mechanically, by the use of metal pins that
are stud welded to the steel substrate. However, it is more
preferable that the mesh does not need pinning to the
substrate.
[0021] For some cellulosic and hydrocarbon fire scenarios, the
reinforcement preferably takes the form of a strip of non
combustible material for example glass tape of approximately 50-150
mm width. This tape would be placed along the "toes" or corners of
a steel section in between usually two coats of the coating of the
present invention. The non-combustible tape has the effect of
preventing the coating from splitting or slumping in a fire when
the coating is applied at the aforementioned 5-6 mm+ and hence
improving the coatings ability to insulate and protect the
underlying steel.
[0022] The coating composition of the invention, in one preferred
embodiment, has a viscosity in the range from 10 poise to 80 poise
measured on a Brookfield Viscometer at 20 degrees Celsius, (but
still retaining 100% or close to 100% non volatile content), hence
facilitating easier application than current existing hydrocarbon
fire protection.
[0023] The coating of the invention generally requires
significantly lower film thicknesses of coating (compared to
current existing products) to provide the same duration of
hydrocarbon fire protection. This not only reduces the cost per
unit area of hydrocarbon fire protection, but also significantly
reduces the weight of coating required and hence reduces the weight
that the steel structure has to bear. Typical coating thicknesses
would be in the range from 0.25 mm to 20 mm and possibly more.
[0024] The coatings of the invention are generally converted to a
solid state significantly quicker than existing prior art
hydrocarbon fire protection coatings, particularly at lower
temperatures, for example below 10.degree. C., where prior art
epoxy type coatings suffer from severe retardation of cure time,
but the present invention does not. Typically this conversion takes
from 20-40 minutes at 25.degree. Celsius to 1-4 hours at
5-10.degree. C.
[0025] It is noted that the liquid intumescent coating composition
may comprise one or more solid components.
[0026] The invention provides a quick-drying coating composition in
that the initiator initiates the conversion of the intumescent
coating composition into a solid state via a free-radical
polymerisation reaction. No organic solvent or water is provided or
is necessary to reduce the viscosity in order to facilitate
application of the coating as this is facilitated by the use of the
reactive monomer. The fact that the coating dries by free radical
polymerisation, as opposed to solvent evaporation also has the
added benefit of giving rise to much higher "solids" content of the
coating, i.e. typically 95-100% by weight of the applied wet
coating becomes dry coating on the substrate, compared to typical
prior art cellulosic coatings where only 60-80% of the applied film
thickness remains in the dry film.
[0027] The coating has particular, but not exclusive application in
the coating of steel structures to provide protection against fire
by forming an intumescent and insulating char. These coatings are
suitable for both on-site and in-shop application.
[0028] Steel sections and other materials that are coated with such
an intumescent coating composition harden much more rapidly than
prior art materials, since the drying time is dependent on the
relatively rapid free-radical chemical reactions rather than on
complete evaporation of volatile components, or chemical curing of
an epoxy system. Drying times are reduced from 24 hours or longer,
to around 60 minutes, (or even less with the incorporation of
additional accelerator). This provides significant benefits to
in-shop applicators, and enables a continuous process of
application, drying and removal of steel sections from the
application area.
[0029] Another benefit is that thick films can be applied in a
single coat application, further reducing drying times compared
with multiple coats of prior art intumescent coatings.
[0030] The present invention utilises free radical cure and
comprises at least one solid thermoplastic polymeric resin
component, combined with lower molecular weight liquid monomeric
(or oligomeric components) containing ethylenically unsaturated
double bonds. Preferably the ethylenically unsaturated double bonds
are present as alpha-beta ethylenically unsaturated carboxylate
ester groups such as methacrylate or acrylate groups.
[0031] The solid thermoplastic polymer is preferably a
(meth)acrylic resin, either as a homopolymer, copolymer or
terpolymer. The polymeric component ideally comprises a
meth(acrylate) copolymer. This may be produced from the
polymerisation of one or more methacrylate and acrylate monomers,
such as any of the following:--methyl methacrylate, ethyl
methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl
methacrylate, 2-hydroxy ethyl methacrylate, 2-hydroxy propyl
methacrylate, 2-ethylhexyl methacrylate and the corresponding
acrylates. Co-reactants may include styrene and vinyl toluene. The
preferred solid thermoplastic polymer is a copolymer of butyl
methacrylate and methyl methacrylate.
[0032] Other options for the solid thermoplastic polymeric resin
component include homopolymers, copolymers or terpolymers derived
from vinyl monomers such as any of the following:--styrene, vinyl
toluene, vinyl chloride, vinyl acetate, vinylidine chloride and
vinyl versatate esters. Co-reactants may include dienes such as
butadiene.
[0033] The solid thermoplastic resin preferably constitutes from
10% to 50% by weight of the resin components of the coating
composition.
[0034] At least one of the liquid monomeric components preferably
contains methacrylate functionality, and most preferably are
methacrylic acid esters. Optionally at least one of the monomeric
components contains acrylate functionality, and most preferably
comprise acrylic acid esters. Additionally the monomeric components
should preferably be monofunctional, in order that the resultant
polymer produced on reaction with an organic peroxide is
thermoplastic and thus melts and flows prior to temperatures at
which the intumescent ingredients react.
[0035] Examples of suitable methacrylic acid esters and acrylic
acid esters include any of the following either alone or in
combination:--methyl methacrylate, ethyl methacrylate, n-butyl
methacrylate, isobutyl methacrylate t-butyl methacrylate,
2-ethylhexyl methacrylate, and the corresponding acrylates. Methyl
methacrylate is most preferred methacrylic acid ester due to its
ability to produce low viscosity solutions of the solid
thermoplastic resin component and its high glass transition
temperature. However, its high volatility and characteristic odour,
may for certain applications mean that alternative methacrylic acid
esters may be preferable. The most preferred acrylic acid ester is
2-ethylhexyl acrylate.
[0036] The liquid monomeric components preferably constitute from
30% to 100% by weight of the resin components of the coating
composition.
[0037] Proprietary resin solutions containing both the
aforementioned solid resin and liquid monomers may also contain
oligimeric components.
[0038] The total resin components ideally constitute from 20% to
60% of the coating composition. More preferably the total resin
components constitute from 25% to 50% of the coating
composition.
[0039] One or more initiators are added prior to use to convert the
liquid coating to a solid state on the substrate. These are
required to initiate the free-radical curing mechanism necessary to
convert the monomeric (and oligomeric) components to a solid state.
The initiators may be AZO compounds, but are preferably one or more
organic peroxides. Suitable classes of organic peroxides include
any of the following either alone or in combination:--diacyl
peroxides, ketone peroxides, peroxyesters, dialkyl peroxides,
hydroperoxides and peroxyketals. Diacyl peroxides are preferred,
the most preferred peroxide in this class being dibenzoyl peroxide,
which may be used in its solid granular form or as a paste with
plasticiser. The preferred form of use is as a paste.
[0040] The organic peroxide composition content is determined by
the total resin content, and preferably constitutes from 0.5% to 5%
of the total resin content. More preferably the organic peroxide
composition constitutes from 1% to 4% of the total resin content.
Note that these figures are based on weight of peroxide proprietary
blend as supplied, containing 50% peroxide as active
ingredient.
[0041] Where dibenzoyl peroxide is used as an initiator, a tertiary
amine is preferably added to the coating compositions to accelerate
the rate of cure, thus allowing the pot-life and curing time to be
optimised. Aromatic tertiary amines are preferred, suitable
examples include any of the following:--N,N-dimethylaniline and
N,N-dialkyl-p-toluidine compounds such as N,N-dimethyl-p-toluidine,
N,N-bis-(2-hydroxypropyl)-p-toluidine and
N,methyl-n-hydroxyethyl-p-toluidine. The most preferred aromatic
tertiary amine accelerators are N,N-dimethyl-p-toluidine. and
N,N-bis-(2-hydroxypropyl)-p-toluidine.
[0042] The tertiary amine content is determined by the total resin
content, and ideally constitutes from 0.1% to 4% of the total resin
content. More preferably the tertiary amine constitutes from 0.25%
to 3% of the total resin content.
[0043] Where an AZO initiator is to be used the preferred
initiators include any of the following either alone or in
combination:--2,2-azobis(amidinopropane)dihydrochloride,
2,2-azobis(2-methylbutyronitrile),
2,2-azobis(2-methylpropanenitrile),
2,2-azobis(2,4-dimethylpentanenitrile). These are available from
Dupont under the trade name of Vazo.
[0044] The intumescent coating compositions of the present
invention also contain specific ingredients that react together
under the influence of heat from a fire, to form a protective
insulating foam or char. These ingredients should be of low
solubility to ensure that the coating has an acceptable level of
durability, and maintains its integrity throughout the service life
of the coating. Additionally, the intumescent ingredients used
should have a sufficiently small particle size, in order to obtain
satisfactory dispersion in the resin components, and thus allow
application by spray application methods giving high rates of
transfer of the coating to the substrate.
[0045] The intumescent ingredients preferably consist of three
components, an acid source, a carbon source and a spumific or gas
source. Preferably an inorganic "nucleating agent" should be
present and optionally additives, which may be solid or liquid in
nature, may be added to aid char formation and strengthen the
char.
[0046] Under the influence of heat (between 100.degree. C. and
200.degree. C.) the resin components melt and begin to flow. As the
temperature increases (>200.degree. C.) the acid source, usually
by decomposition, produces copious amounts of acid which can react
with other constituents in the coating. If the acid source is
ammonium polyphosphate, polyphosphoric acids are released which can
react with polyhydric alcohols such as pentaerythritol (carbon
source) to form polyphosphoric acid esters. The decomposition of
these esters leads to the formation of carbon compounds, which
together with a blowing agent such as melamine, give rise to a
carbon foam or char.
[0047] The intumescent coating compositions of the present
invention ideally contain at least one acid source, examples of
which include ammonium polyphosphate, melamine phosphate, magnesium
sulphate and boric acid. The preferred acid source is ammonium
polyphosphate.
[0048] Ammonium polyphosphate can vary in molecular weight (chain
length), the lower the molecular weight, the higher the solubility.
By having very high molecular weight and a cross-linked structure
it is possible to have very low water solubility, though higher
thermal stability is observed. Coating ammonium polyphosphate with
silane, melamine or melamine formaldehyde is beneficial in further
reducing solubility and can also lead to higher loadings due to a
reduction in resin absorbing properties. The use of coated ammonium
polyphosphate is preferred, and ammonium polyphosphate coated with
melamine formaldehyde is most preferred.
[0049] The acid source preferably constitutes from 35% to 65% by
weight of the intumescent ingredients content of the coating
composition.
[0050] The intumescent coating compositions of the present
invention ideally contain at least one carbon source, examples of
which include polyhydric alcohols such as pentaerythritol, and
dipentaerythritol. Starch and expandable graphite are other
possible carbon sources. The preferred carbon sources are
pentaerythritol and dipentaerythritol or a combination of the
two.
[0051] The carbon source preferably constitutes from 5% to 40% by
weight of the intumescent ingredients content of the coating
composition.
[0052] The intumescent coating compositions of the present
invention ideally contain at least one gas source, examples of
which include any of:--melamine, melamine phosphate, melamine
borate, melamine formaldehyde, melamine cyanurate,
tris-(hydroxyethyl) isocyanurate (THEIC), ammonium polyphosphate or
chlorinated paraffin. The resin itself may be a gas source as it
undergoes decomposition. The preferred gas source is melamine.
[0053] The gas source preferably constitutes from 5% to 40% by
weight of the intumescent ingredients content of the coating
composition.
[0054] Although not an essential ingredient in intumescent
reactions, inorganic "nucleating" agents are a preferred ingredient
since they promote sites for the intumescent char to form, improve
the thermal resistance properties and stability of the intumescent
char during a fire. The intumescent coating compositions of the
present invention ideally contain at least one nucleating agent,
examples of which include titanium dioxide, zinc oxide, aluminium
oxide, silica, metal oxides such as cerium oxide, lanthanum oxide
and zirconium oxide, mica and bentonite clay. A preferred
nucleating agent is titanium dioxide which also provides opacity to
the coating
[0055] The nucleating agent preferably constitutes from 1% to 25%
by weight of the intumescent ingredients content of the coating
composition. Further optional additives may be optionally included
as part of the intumescent ingredients to aid char formation and to
strengthen the char and prevent char degradation especially in
jetfire scenarios. Such additives include solids such as zinc
borate, zinc stannate, zinc hydroxystannate, glass flake, glass
spheres, polymeric spheres, fibres (ceramic, mineral, glass/silica
based), aluminium hydroxide, antimony oxide, boron phosphate, fumed
silica.
[0056] The total intumescent ingredients ideally constitute from
40% to 85% of the total coating composition. More preferably the
total intumescent ingredients constitute from 50% to 75% of the
total coating composition.
[0057] In order that the intumescent coating compositions of the
present invention can be applied at high film thickness in a single
coat application it is preferred to modify the rheology of the
coating by the incorporation of a thixotrope. Suitable thixotropic
additives include organically modified inorganic clays such as
bentonite clays, hectorite clays or attapulgite clays, organic wax
thixotropes based on castor oil and fumed silica. The most
preferred thixotropic additives are wax thixotropes and fumed
silicas.
[0058] The thixotropic additive preferably constitutes from 0% to
2% of the total coating composition. A more preferred level is from
0.05% to 1%.
[0059] To improve or facilitate dispersion of the intumescent
ingredients and also to reduce the overall viscosity of the
intumescent coating, it may be necessary to incorporate
wetting/dispersion additives. Such additives are usually liquid in
form and can be supplied either containing a solvent or be solvent
free. Where required preferably a solvent free wetting agent is
used, even more preferably a wetting agent with acid functionality
is recommended, at levels between 0%-2% by weight of the
intumescent coating composition
[0060] The components of the intumescent coating compositions, with
the exception of the organic peroxide initiator, are preferably
blended together by the coating manufacturer using high speed
dispersion equipment, whereby the solid intumescent ingredients are
wetted out and dispersed in the resin components. Optional
dispersion aids may be incorporated to facilitate this process.
[0061] The thickness of the coating is ideally at least 250
.mu.m.
[0062] Prior to application of the coating the organic peroxide is
incorporated into the bulk of the liquid coating. This initiates
the free radical reactions that will convert the liquid coating to
its solid state. Typically, the initiated liquid coating will
remain liquid and suitable for application for up to 30 minutes,
though this can be modified by varying the quantities of initiator
and accelerator in the formulation.
[0063] Suitable preferred methods of application of the aforesaid
compositions include airless spray, brush, roller, trowel and
dipping. Airless spray is most preferred. Airless spray pumps
having a ratio of 45:1 or greater, and preferably 60:1 are
suitable. A minimum air pressure of greater than 60 p.s.i. and
preferably 80 p.s.i. is required, and the compositions are sprayed
using a tip size ranging from 0.015 inch and 0.035 inch.
[0064] An alternative method of application can be by means of a
plural component spray system. This can be achieved in two ways, as
set out below:--
1. The initiator (peroxide) component of the coating composition
and the main (base) component are pumped separately in the correct
ratio through fluid lines to a mixing device. This device mixes the
two components automatically and then dispenses the mixed
homogenous coating down a further fluid line to the spray tip where
the coating is applied as per the above mentioned airless spray
application. 2. The second method involves the initial manufacture
of two batches of coating. One batch comprises a coating containing
no amine accelerators, the other batch comprising a coating
containing double the original level of amine accelerators. Prior
to application double the original level of initiator (peroxide) is
mixed with the batch containing no amine accelerators. The two
components are then mixed in the fluid line by plural component
spray equipment, but at a more manageable 1:1 mixing ratio (opposed
to approximately 50-200:1 previously). The in-line mixed liquid
coating will have the right level of amine accelerators and
initiator (peroxide). In view of the lack of amine accelerators in
the batch containing the peroxide, this batch has a much extended
use or pot life, typically up to 24 hours thus providing sufficient
time to apply all of the mixed material.
[0065] The coating compositions should be stored under cool
conditions, and ideally application should only be carried out
under such conditions. Where it is necessary to apply the coating
compositions at higher temperatures, then modified formulations
that have been adjusted for initiator or accelerator should be
used.
[0066] The coating compositions of the present invention can be
applied in liquid form to steel sections up to several metres in
length with a gauge thickness typically ranging from 5 mm to 30 mm
or greater. Depending on the Hp/A of the steel section coating can
be applied at the required thickness to achieve up to 120 minutes
fire protection.
[0067] Steel sections requiring fire protection are normally blast
cleaned prior to the application of an intumescent coating to
remove millscale and other deposits that may lead to premature
failure of the intumescent coating, either on prolonged atmospheric
exposure or during a fire situation. In order to prevent
deterioration of the blast cleaned surface, particularly where
there is a delay in applying the intumescent coating, it is normal
practice to apply a primer coating. This is often the case when the
intumescent coating is applied on site.
[0068] Examples of suitable primers are coatings based on epoxy,
modified epoxy (such as modified with polyvinyl butyral),
polyurethane, acrylic, vinyl and chlorinated rubber. Primers based
on epoxy are preferred.
[0069] The thickness of the primer is ideally in the range from 15
microns to 250 microns. Preferably the thickness should be in the
range from 25 microns to 100 microns.
[0070] A decorative topcoat may be applied to the cured intumescent
coatings of the present invention, particularly to provide colour
to exposed steelwork. A topcoat if correctly formulated will also
enhance the durability of the intumescent coating compositions. A
clear sealer may also be suitable.
[0071] Examples of suitable decorative topcoats are coatings based
on epoxy, polyurethane, alkyd, acrylic, vinyl and chlorinated
rubber. Decorative topcoats based on polyurethane and acrylic are
preferred.
[0072] The thickness of the decorative topcoat can vary from 15
microns to 250 microns. Preferably the thickness should be in the
range from 25 microns to 75 microns, as too high a thickness of
topcoat may inhibit the intumescent reactions.
[0073] In order that the present invention may be more readily
understood, some specific examples thereof are set out below.
TABLE-US-00001 Example formulation: 1 Parts by weight. Component A
Titanium dioxide 9.80 Ammonium polyphosphate 29.00 Pentaerythritol
8.20 Melamine 10.50 Castor oil based thixotrope 0.70 (Meth)acrylic
resin 31.60 Methyl methacrylate monomer 10.20 100.00 Component B
Dibenzoyl Peroxide paste (50% in plasticiser) 1.0
[0074] Mix component B thoroughly into component A immediately
prior to application
Example Formulation 2
TABLE-US-00002 [0075] Example formulation: 2 Parts by weight
Component A Titanium Dioxide 9.52 Fumed Silica 0.14 Pentaerythritol
8.89 Zinc Borate 1.01 Melamine 14.84 Aluminium Hydroxide 0.51
Ammonium Polyphosphate 31.6 Wetting Agent 0.38 (meth)acrylic resin
33.11 Component B Dibenzoyl Peroxide paste 1.0
[0076] Mix component B into component A immediately prior to
application
Test 1.
[0077] The above example formulations were applied to a 1/2 metre
steel I-section having a web length of 203 mm, a flange length of
203 mm and a weight of 52 kg per metre (Hp/A=180). The mean dry
film thickness was measured at 1625 microns for example 1 and 2500
microns for example 2, after being allowed to dry for 5 days.
[0078] The steel section was fire-tested in a 1 m.sup.3 furnace
according to BS476 Part 20, 1987 cellulosic heating curve The time
taken for the steel section to reach the Critical Failure
Temperature (550.degree. C.) was 63 minutes for example formulation
1 and 83 minutes for example formulation 2
[0079] The above example formulation was applied by a plural
component spray system to a 1 metre steel I-section column having a
web length of 254 mm, a flange length of 254 mm and a weight of 132
kg per metre (Hp/A=98). The mean dry film thickness was measured at
3650 microns, after being allowed to dry for 5 days.
[0080] The steel section was fire-tested in a 4 m.sup.3 furnace
according to BS476 Part 20, 1987 (cellulosic heating curve). The
time taken for the steel section to reach the Critical Failure
Temperature (550.degree. C.) was 116 minutes.
[0081] An example formulation was applied by a plural component
spray system onto two 1 metre steel I-section columns having a web
length of 254 mm, a flange length of 254 mm and a weight of 73 kg
per metre (Hp/A=171). The mean dry film thickness was measured at
5050 microns for column 1 and 5150 microns for column 2, after
being allowed to dry for 5 days. Column 2 was prepared as column 1
but with the incorporation of a 100 mm wide strip of self-adhesive
glass tape along the toes or corners of the column in between 2
coats of the coating.
[0082] Reference is made to the drawings in which:--
[0083] FIG. 1 is a cross-section through the coated metre steel
I-section described with reference to column 2 of test 2: and
[0084] FIG. 2 is a perspective view of the steelwork shown in FIG.
1 to which only the first coating and mesh reinforcement is
applied.
[0085] In the drawings a steel column 10 is coated with a first
coating layer 11 and a second coating layer 12. Reinforcement
adhesive-coated glass mesh tape 13 of 100 mm width is placed on the
corners or "toes" of the column prior to the second coating being
applied.
[0086] The steel sections were fire-tested in a 1 m.sup.3 furnace
according to the UL 1709 hydrocarbon heating curve. The time taken
for column 1 to reach Critical Failure Temperature (538.degree. C.)
was 82 minutes. However, one area of the column (one of the corners
or toes) reached the single area failure limit of 649.degree. C. at
67 minutes and this was taken to be the actual failure time. Column
2 reached the critical failure temperature (538.degree. C.) after
102 minutes, there was no upper temperature limit failure.
[0087] It is to be understood that the above-described embodiment
is by way of example only. Many modifications and variations are
possible.
* * * * *